U.S. Navy watertight arrangements are utilized in watertight boundaries where personnel egress through bulkheads is needed but watertight integrity must be maintained. The sealing mechanism of standard watertight door arrangements comprise a series of dogs sliding across ramped wedges, which are connected to the door panel. The sliding of the dogs across the wedges pulls the panels into a knife edge associated with the door. Navy protocol requires that the knife edge must compress the gasket to one-eight of an inch in order for the door system to be deemed watertight.
Until the 1990s, the Navy used primarily three types of gaskets in watertight arrangements: Military Specification Mil-R-900 (rubber gasket material); Federal Specification ZZ-R-765 (silicone rubber, Class 2b Grade 40); and, Military Specification Mil-G-17927 (gaskets, glass-metallic cover with silicone core). The Military Specification Mil-R-900 gaskets were designed with a generally rectangular cross section in which two edges were chamfered. These gaskets had a high durometer rating, requiring excessive dogging forces needed to correctly seal the door. These high dogging forces resulted in accelerated wear on watertight door components, requiring extensive adjustment and replacement of door components such as wedges and linkage bearings. Additionally, these gaskets were difficult to install and even more difficult to remove.
The type ZZ-R-765 gaskets were typically used in watertight doors in missile blast areas. The ZZ-R-765 gaskets were also designed with a generally rectangular cross section in which two edges were chamfered. These gaskets had a generally low durometer rating, and were mid-range with respect to costs. For watertight applications, the ZZ-R-765 gaskets were relatively easy to install and remove.
The type Mil-G-17927 gaskets had a silicone core and two additional layers of glass metallic-cloth, topped by a silicone rubber coating. The Mil-G-17927 gaskets had a generally rectangular cross section. These gaskets had a high durometer rating and were extremely expensive to procure.
If fire and smoke protection are required in addition to water protection, then the gaskets must be able to withstand temperatures of about 2000 degrees Fahrenheit and maintain their fire, smoke, and water sealing integrity. Of the three gaskets types named above, the ZZ-R-765 Class 2B Grade 40 performed best, however there was still a need for improvement. In light of this need, a new watertight door gasket, outlined in U.S. Pat. No. 5,553,871, was developed using Federal Specification ZZ-R-765 as the material requirement. Eventually, this Federal Specification became obsolete and was replaced by Commercial Item Description A-A-59588. This new gasket had an altered profile with a generally rectangular cross section with chamfered edges, and a semi-circular cut-out portion along a surface. This design allowed for easier dogging of watertight door panels and improved fire and smoke protection. However, this gasket design still failed to properly seal exits when exposed to fires of about 1,500 to 2,000 degrees Fahrenheit for prolonged periods of time. Consequently, there is still a need for a seal with a design that protects against the entry of fire, smoke, and water, especially when exposed to fires of from about 1,500 degrees Fahrenheit to 2,000 degrees Fahrenheit and higher.